A high growth in hurricane-induced losses in recent years is a significant concern for coastal communities. Low-rise buildings, including residential structures, institutional structures, and commercial structures, are believed to be a dominant building type in the United States and also seem to be among the most vulnerable under high winds, such as those occur during hurricanes, tropical storms, etc. Recent post-disaster surveys have provided direct evidence that hurricane-induced damage and property losses are caused in large part due to failure of roofs and subsequent intrusion of water into a building.
Wind damage to buildings principally manifests in breach of the roof envelope and/or the wall envelope, and consequent damage to the building contents. Hence, the vulnerability of buildings to high winds is a function of the loading and the strength of building envelope components and their connections. Also, for a given building impacted by winds of a given intensity, the resulting damage is largely dependent upon the nature of its immediate environment and the architectural design of the building.
Extreme wind events are responsible for significant property damage and loss of life due to compromised residential homes. Hurricanes, for example, create massive destruction, and the damage from the wind pressure, wind borne debris, storm surge, and flooding cause high losses over a short period of time. Coastal areas in the United States along the Atlantic and Pacific Oceans and the Gulf of Mexico are particularly susceptible to this type of damage. Other extreme wind events may include tornados, high straight line wind storms, and typhoons, along with katabatic winds, such as the Santa Ana winds in California.
If the building envelope is compromised, the whole structure is put in jeopardy, because internal pressure results. While wind pressure creates high forces, especially near the edges of the structure, wind borne debris can also compromise the structure. The roof system of the building is particularly of interest because the construction methods create a component of the overall structure that is a potentially weaker point.
For example, damage investigation following Hurricane Andrew in 1992 and other more recent events found that many building structures were not destroyed because of the external wind-pressure load alone. Flying debris frequently breached the windward elements of the building envelopes and subjected the building interior to intense fluctuations of positive pressure. However, fluctuating negative pressure on exterior surfaces, in combination with the positive internal pressure, results in significantly larger forces on some components of the building envelope than would be caused by external pressure alone. Therefore, the likelihood of simultaneous occurrence of a positive internal pressure and a negative external pressure peak is of major importance in building design considerations.
Historically, damage to roof coverings and rooftop equipment is the leading cause of building performance problems during hurricanes. Rains accompanying a hurricane can cause water to enter buildings through damaged roofs, resulting in major damage to the contents and interior. For example, unless quick action is taken to dry a building, mold bloom can quickly occur in the hot, humid Florida climate. Drying of buildings was hampered after Hurricane Charley in 2004 by the lack of electrical power to run fans and dehumidifiers. These damages frequently are more costly than the roof damages themselves. Water leakage can also disrupt the functioning of critical and essential facilities and weaken ceilings and cause them to collapse. Further, ceiling collapse can cause injury to occupants.